In present communication systems, generally only one communication entity is allowed to send signals with a communication parameter, otherwise signal interference is most likely to occur. Therefore, each communication entity, before sending the signals, needs to first submit a sending request. When the sending request is acknowledged, the communication entity can send the signals with the appointed communication parameter.
In view of the above, a Secondary Protective Device (SPD), before sending information, needs to send a Request to Send (RTS) sequence to a Primary Protective Device (PPD). The RTS sequence sent by each SPD has the same contents.
When receiving only one RTS sequence at a given time, the PPD sends responses corresponding to the received RTS sequence to all the SPDs. Then the SPD sending the RTS sequence determines that the right to speak is obtained on receiving the response, and subsequent operations such as sending information may be performed. The other SPDs receiving the response determine that the right to speak is not obtained and need to resend the RTS sequence to the PPD after waiting for a period of time.
When receiving multiple RTS sequences at the same time, the PPD sends Negative Acknowledgment (NACK) responses to all the SPDs. And then each of the SPDs determines that the right to speak is not obtained on receipt of response and that each of the SPDs needs to resend the RTS sequence to the PPD after waiting for a period of time.
Obviously, in the above scheme, the efficiency of determining the right to speak for the SPD is low. When multiple SPDs need to send information at the same time, the RTS sequences of all the SPDs may be refused. In this case, the problem of the low efficiency of determining the right to speak is more serious, thus satisfaction of users is badly affected.